Errr... I think you have quoted the wrong person because you'll note I said nothing about Sandbox and everything about how horridly slow the main story development as been.
Look, I am all in for the Dev to have some character growth and all... BUT IT HAS BEEN YEARS since the last bit of significant main story progress. Missus Powell has been kidnapped years ago for us players, its a Hell of a long time without resolving the main storyline, you know how it should have been done?
Do the main storyline at least until the next major story thread is concluded and fluff the character growth afterward, making it all in a way where you are not effectively locked out of the main story developing for WAY too long, its the one benefit of going for the Sandbox system, you don't need to go for developing your story linearly as much as a normal VN, which the Dev as ignored and instead decided to make everything linearly, which at this point he might as well have made it a normal VN if that was going to be the case.